JP2022071283A - Slide mechanism - Google Patents

Abstract

To provide a slide mechanism including a slide member with a carbon-containing coating film, having high adsorption performance to a lubricant including a molybdenum extreme pressure additive, and high friction reduction effect by molybdenum disulfide.SOLUTION: A slide mechanism includes a slide member having a DLC-Ni coating film including metal nickel in a DLC film, on a surface, and a lubricant existing on a slide surface of the slide member. A carbon film is a DLC-Ni coating film having DLC as its main component and including nickel (Ni), the lubricant includes a molybdenum (Mo)-containing compound, and friction reduction effect by a reaction coating film having molybdenum disulfide can be also obtained, in addition to low friction characteristic of the DLC film itself.SELECTED DRAWING: Figure 1

Description

The present invention relates to a sliding mechanism, and more particularly to a sliding mechanism including a sliding member having a carbon-containing coating capable of sufficiently exerting a friction reducing ability by a lubricating oil.

Diamond-like carbon (DLC) film is a long-life solid lubricating film that combines extremely low friction properties with high hardness. It is considered that the low friction property of the DLC film is due to the fact that shearing easily occurs at the contact interface with the sliding mating material due to the small adhesive force of the surface.

However, since the adhesive force of the DLC film is very small, it is difficult to form a sufficient oil film on the surface of the DLC film in a sliding mechanism such as an internal combustion engine or a transmission in which lubricating oil is present.

Therefore, it is difficult to obtain the friction reducing effect of the lubricating oil even in the presence of the lubricating oil, and the friction characteristics of the sliding mechanism are largely due to the friction characteristics of the DLC film.

It is known that even such a DLC film can obtain further low friction by combining it with a lubricating oil containing an ester-based molecule.

Further, a molybdenum-based extreme pressure additive containing organic molybdenum, sulfur, or the like is often added to the lubricating oil of an internal combustion engine or a transmission.

In the molybdenum-based extreme pressure additive, a reaction film containing molybdenum disulfide (MoS ₂ ) having a layered structure having a very small shearing force between layers is formed on the sliding surface by sliding, and the layers of the molybdenum disulfide are formed between the layers. Sliding reduces friction.

However, Patent Document 1 describes that when the surface of the sliding member is covered with the DLC film, the reaction film is not formed and the friction reducing effect of the reaction film cannot be obtained.

Therefore, Patent Document 1 discloses that by using an iron-containing DLC film in which iron is exposed on the surface, the reaction film is formed on the sliding surface and friction can be reduced.

Japanese Unexamined Patent Publication No. 2000-320673

However, in the case described in Patent Document 1, the adsorptivity of the iron-containing DLC film to the lubricating oil containing the molybdenum-based extreme pressure additive is still poor, and the friction reducing effect of molybdenum disulfide cannot be sufficiently exhibited.

The present invention has been made in view of the problems of the prior art, and an object of the present invention is to have high adsorption ability to a lubricating oil containing a molybdenum-based extreme pressure additive, and friction due to molybdenum disulfide. It is an object of the present invention to provide a sliding mechanism provided with a sliding member having a carbon-containing film, which has a high reduction effect.

As described in Patent Document 1, the reaction film containing molybdenum disulfide (MoS ₂ ) is not formed by the sliding member coated with the DLC film. Therefore, the molybdenum-based extreme pressure additive alone does not form the reaction film. Is not formed, and it is considered that other elements such as iron are involved in the formation of the above reaction film.

However, since the structures of lubricating oils and extreme pressure additives are extremely complicated and there are innumerable combinations of these materials, it is extremely difficult to chemically elucidate the formation process of the above reaction film. It is not possible to specify an element useful for forming the above reaction film from the regular elemental properties obtained from the above.

As a result of repeated tests and studies on various elements in order to achieve the above object, the present inventor has formed a carbon-containing film on the surface of the sliding member as a DLC-Ni film in which metallic nickel is contained in the DLC film. By doing so, it was found that the above object could be achieved, and the present invention was completed.

That is, the sliding mechanism of the present invention includes a sliding member having a carbon-containing film on the base material, and lubricating oil existing on the sliding surface of the sliding member.
The carbon-containing film is a DLC-Ni film containing DLC as a main component and nickel (Ni), and the lubricating oil is characterized by containing a molybdenum-containing (Mo) compound.

According to the present invention, since the DLC-Ni film containing metallic nickel in the DLC film is formed on the surface of the sliding member, the reaction having molybdenum disulfide in addition to the low friction characteristics of the DLC film itself. It is possible to provide a sliding mechanism provided with a sliding member having a carbon-containing coating, which can also obtain a friction reducing effect due to the coating.

It is a figure which shows the layer structure of the distributed DLC-Ni film. It is a figure which shows the layer structure of the laminated DLC-Ni film. It is a figure which shows the layer structure of the multi-layer laminated type DLC-Ni film. It is an SEM image of a DLC film. It is the XPS analysis result of the sliding member surface of Example 1. It is the XPS analysis result of the sliding member surface of Example 3.

The sliding mechanism of the present invention will be described in detail.
The sliding mechanism includes a sliding member having a DLC-Ni film having a DLC-Ni film containing metallic nickel on the surface of the DLC film, and a lubricating oil existing on the sliding surface of the sliding member. It is a DLC-Ni film containing DLC as a main component and nickel (Ni), and the lubricating oil contains a molybdenum-containing (Mo) compound.
In the present invention, the "main component" is 50 at% or more.

<DLC-Ni coating>
The reason why the DLC-Ni coating of the present invention has a high affinity with the lubricating oil containing a molybdenum-containing (Mo) compound and can increase the friction reducing effect is not clear, but the Ni in the DLC-Ni coating is molybdenum-based. It reacts with sulfur (S) in the extreme pressure additive to form sulfides such as NiS and _NiS2 . This sulfide has a high affinity for Ni in the DLC-Ni film and serves as a source of sulfur for molybdenum (Mo), so that a reaction film containing molybdenum disulfide (MoS ₂ ) can be easily formed. Is also considered to be one of the causes.

The DLC-Ni coating preferably has a hydrogen content of 1 at% or less.
A hydrogen-free DLC film having a hydrogen content of 1 at% or less has high hardness and high heat resistance, and has an excellent effect of reducing the coefficient of friction in the presence of lubricating oil.

The DLC-Ni coating includes a dispersed DLC-Ni coating in which nickel (Ni) is dispersed as shown in FIG. 1, and a laminated DLC-Ni in which a DLC film and a metallic nickel film are laminated as shown in FIG. The film may be mentioned, and the laminated DLC-Ni film may have a multilayer structure in which a plurality of DLC films and metallic nickel films are alternately laminated as shown in FIG.

(Distributed DLC-Ni coating)
In the dispersed DLC-Ni film, Ni atomic masses in which several to several tens or more are gathered are uniformly finely dispersed in the DLC film, and a reaction film is formed on the entire sliding surface.

The Ni content in the dispersed DLC-Ni film is preferably 1 to 15 at%, more preferably 2 to 10 at%, and even more preferably 3 to 5 at%.

In the dispersed DLC-Ni coating, when the Ni content is large, a reaction coating is easily formed and a friction reducing effect is obtained, but the hardness of the coating tends to decrease, which is high within the above range. Both friction reduction effect and wear resistance can be achieved.
The Ni content can be measured by energy dispersive X-ray analysis (EDX).

The dispersed DLC-Ni film can be produced by an ion plating method using graphite mixed with Ni as a target material or a plasma CVD method using a gas containing Ni and a hydrocarbon gas. The Ni content can be controlled by changing the conditions during film formation, in addition to the amount of Ni powder mixed with graphite and the amount of gas containing Ni.

(Laminated DLC-Ni coating)
Unlike the dispersed DLC-Ni film, the laminated DLC-Ni film has high durability because Ni is not dispersed in the underlying DLC film, so that the hardness of the DLC film itself does not decrease.

The thickness of the Ni layer laminated on the DLC film of the laminated DLC-Ni film is preferably 0.1 to 1 μm, more preferably 0.3 to 0.7 μm. The thickness of the DLC film is not particularly limited, but is preferably thicker than the Ni layer.

If the Ni layer becomes too thick, the effect of reducing the contact area due to the hardness of the lower DLC film tends to be diminished. Within the above range, deformation of the Ni layer due to the load is suppressed, and both prevention of increase in the coefficient of friction and high friction reduction effect can be achieved at the same time.

In the laminated DLC-Ni film, it is preferable that the lower DLC film has recesses.
In the laminated DLC-Ni coating, the upper Ni layer formed on the surface side is first worn by sliding. However, since a part of the upper Ni layer penetrates into the recess of the lower DLC film to form a film, even if the upper Ni layer is worn and the lower DLC film is exposed, it is rubbed by the Ni in the recess. A reduction effect can be obtained. In addition, since Ni in the recess is surrounded by DLC, it is difficult to wear even if it is exposed on the surface, so that a friction reducing effect can be obtained for a long period of time.

The area ratio of the recesses on the surface of the DLC film is preferably 4 to 60%, more preferably 10 to 50%, and further preferably 15 to 40%.

When the area ratio of the recess is within the above range, it is possible to achieve both the wear resistance of the DLC film and the formation of the reaction film by Ni.

For the above area ratio, after removing Ni by concentrated hydrochloric acid or dilute nitric acid treatment, 3D roughness measurement is performed with a laser microscope (ISO 25178), and SMr2 of the abbott load curve showing the ratio of valleys is used with a roughness meter. It can be calculated from the measured cross-sectional curve.
Alternatively, as another method, the laminated DLC-Ni can be calculated by performing element mapping from the surface in a state where the laminated DLC-Ni is sufficiently blended by friction, and binarizing the obtained image with respect to Ni.

The laminated DLC-Ni film can be produced by forming a DLC film by a plasma CVD method or an ion plating method and then depositing a Ni layer on the DLC film by sputtering or the like.

The recesses on the surface of the DLC film can be formed by ion etching laser treatment, blast treatment, or by preliminarily making irregularities on the surface of the base material. In particular, since the DLC film formed by the ion plating method is made of graphite, droplets are formed on the surface of the DLC film. When this is removed by polishing, a recess can also be formed by making the contact of the abrasive with the above-mentioned droplet non-uniform.

<Lubricating oil>
The lubricating oil in the sliding mechanism of the present invention contains a base oil and a molybdenum-based extreme pressure additive containing a molybdenum-containing (Mo) compound.

As the base oil, those conventionally used for sliding engines such as internal combustion engines and transmissions can be used, and either mineral oil or synthetic oil may be used.
Among them, a base oil having a polar group such as a higher fatty acid, a higher alcohol, an aliphatic amine, or an ester at one end of a molecule can be preferably used because the polar group forms an adsorption film on the metal surface by physical adsorption or chemical adsorption. ..

Examples of the molybdenum-based extreme pressure additive include organic molybdenum containing sulfur such as molybdenum dithiocarbamate (MoDTC).

<Mother material>
It is generally known that a sliding mechanism in which materials of the same type are combined has a large frictional force. It is considered that this is because when the same kind of materials are combined, adhesion is likely to occur due to the high affinity thereof. Therefore, the friction reducing effect expected that the mating material is a DLC film or a sliding member containing Ni cannot be obtained.

In the sliding mechanism of the present invention, it is preferable that the mating material of the sliding member contains iron (Fe).
The molybdenum-based extreme pressure additive in the lubricating oil is originally used to reduce the friction of the iron-based sliding member, and is a solid wettable agent by a chemical reaction with iron on the sliding surface of the iron-based sliding member. Produces a reaction film containing MoS ₂ that functions as Therefore, when the mating material contains iron (Fe) instead of Ni, an excellent friction reducing effect can be obtained in combination with the low affinity with the DLC-Ni film and the formation of the reaction film.

Further, the mating material containing iron (Fe) forms iron sulfide such as FeS and Fe 3S in the presence of a molybdenum _{-based extreme pressure additive, and serves as a supply source of S of MoS 2 which} is a solid lubricating layer. It acts on the formation, and the formation of iron oxide films such as FeO, _{Fe2O3 ,} and _Fe3O4 has the function of promoting and stabilizing the formation of MoS ₂ , which is a solid lubricating layer, _on the upper layer, which causes friction. It works to enhance the effect of reduction.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
By plasma CVD method using a gas containing Ni and a hydrocarbon gas, a disc of SUJ2 carbon steel (HRC64) having a surface roughness (Ra) of 0.01 μm contains 4.5 at% Ni, and the film thickness is 1 μm. , A dispersed DLC-Ni film (a-C: H) having a surface roughness (Ra) of 0.01 μm was formed.

[Example 2]
Dispersed DLC-containing 5 at% Ni by ion plating method using a target material containing metallic Ni in graphite on a disc of SUJ2 carbon steel (HRC64) having a surface roughness (Ra) of 0.01 μm. After forming the Ni film, the droplets were removed by polishing to form a dispersed DLC-Ni film (ta-C) having a surface roughness (Ra) of 0.02 μm and a film thickness of 1 μm.

[Comparative Example 1]
A dispersed DLC-Ti film (ta) having a surface roughness (Ra) of 0.02 μm is the same as in Example 2 except that graphite containing Ti is used as the target raw material and 5 at% of Ti is contained by the ion plating method. -C) was formed.

[Comparative Example 2]
A dispersed DLC-Cu film (ta) having a surface roughness (Ra) of 0.02 μm is the same as in Example 2 except that graphite containing Cu is used as the target raw material and 5 at% Cu is contained by the ion plating method. -C) was formed.

[Example 3]
Using graphite as the target material, a DLC film (ta-C) is formed on a disc of SUJ2 carbon steel (HRC64) having a surface roughness (Ra) of 0.01 μm by the ion plating method, and the droplets are polished. A DLC film having a surface roughness (Ra) of 0.02 μm and a film thickness of 0.5 μm was obtained.
The SEM image of the DLC film is shown in FIG. This DLC film had recesses, and the area ratio thereof was 15%.

A Ni layer having a thickness of 0.5 μm was deposited on the DLC film by sputtering to form a laminated DLC-Ni film (ta-C) having a surface roughness (Ra) of 0.02 μm.

<Evaluation>

A DLC film (a-C: H, Reference Example 1) formed by the plasma CVD method and an ion play as a reference disk as a reference disk for evaluating the friction reduction effect in consideration of the difference in friction characteristics due to the difference in film quality. The surface roughness (Ra) of the DLC film (ta-C, Reference Example 2) formed by the Ting method was adjusted to 0.01 μm and 0.02 μm, respectively, and used as a reference disk.
The friction coefficient of the discs of Examples 1 to 3 and Comparative Examples 1 and 2 was measured under the following conditions, and the friction characteristics (friction reduction effect) of the disc were evaluated by the difference in the friction coefficient from the reference disk.
The evaluation results are shown in Table 1.

(Lubricant)
A lubricating oil obtained by adding 750 ppm of MoDTC to a commercially available engine oil (Pens Oil Platinum 0W-20 API SN ILSAC GF-5, 40 ° C. kinematic viscosity 45 mm ² / s, 100 ° C. kinematic viscosity 8.4 mm ² / s) was used.

(Mother material)
SUJ2 carbon steel (HRC64) pin (surface roughness Ra: 0.05 μm)

(Friction test)
Disc Φ31 t = 2.5mm, pin Φ5x5mm, 3 points 1 set Oil bath type Oil temperature: 120 ℃
Test time: 30 minutes Test load: 90N (Hertz maximum surface pressure 150MPa)
Test rotation speed: 30 rpm
Average sliding radius: Approximately 10 mm
The value of the coefficient of friction at the end of the test was taken as the coefficient of friction.

Further, the disc surfaces of Example 1 (dispersion type DLC-Ni coating) and Example 3 (laminated DLC-Ni coating) after the friction test were analyzed by XPS.
The analysis result of Example 1 is shown in FIG. 5, and the analysis result of Example 3 is shown in FIG.

From FIGS. 5 and 6, it can be seen that in the sliding mechanism of the present invention, a compound containing nickel sulfide such as NiS is present on the sliding surface and acts on the formation of the reaction film derived from MoDTC.

Further, from the results in Table 1, the film on which the DLC-Ni film is formed has a smaller coefficient of friction than the reference disk, and in addition to the low friction characteristics of the DLC film itself, the friction due to the reaction film having molybdenum disulfide. It was confirmed that the reduction effect was obtained.

1 Sliding member 2 Base material 3 DLC-Ni coating 31 DLC
32 Ni

Claims (9)

A sliding member having a carbon-containing film on the base material,
A sliding mechanism provided with lubricating oil existing on the sliding surface of the sliding member.
The carbon-containing film is a DLC-Ni film containing diamond-like carbon (DLC) as a main component and nickel (Ni).
A sliding mechanism characterized in that the lubricating oil contains a molybdenum-containing (Mo) compound. The sliding mechanism according to claim 1, wherein the DLC-Ni coating has a hydrogen content of 1 at% or less. The sliding mechanism according to claim 1 or 2, wherein the DLC-Ni film is a dispersed DLC-Ni film in which nickel (Ni) is dispersed in the DLC film. The sliding mechanism according to claim 3, wherein the dispersed DLC-Ni coating has a nickel (Ni) content of 1 to 15 at%. The sliding mechanism according to claim 1 or 2, wherein the DLC-Ni film is a laminated DLC-Ni film having a nickel (Ni) layer on the surface of the DLC film. The sliding mechanism according to claim 5, wherein the laminated DLC-Ni film has a nickel (Ni) layer having a thickness of 0.1 to 1 μm. The sliding mechanism according to claim 5 or 6, wherein the DLC film has a recess and the area ratio thereof is 4% or more. The sliding mechanism according to any one of claims 1 to 7, wherein the mating material of the sliding member contains iron (Fe). The sliding mechanism according to claim 8, wherein the sliding surface has a compound layer containing nickel sulfide (NiS), molybdenum disulfide (MoS ₂ ), and triiron tetroxide (Fe _{3O 4 )} .

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